The printing of substrates, such as woven and nonwoven fabrics and films, is well known. The printing of fabrics with inks and dyes is a common and widely used method for imparting patterns and colors to a basic fabric. Many current products, such as diapers and training pants, include printed designs to improve their appearance. A problem with such printed products is that the printed design can be smeared or even removed during the handling of products during manufacturing, packaging, and use.
Pigmented inks are beneficial for use on substrates because they tend to be more resistant to leaching and mechanical rubbing than dye-based inks and thus tend to be more resistant to being removed from the surface of substrates. Pigment-based inks also have better optical density per unit weight (better “mileage”) than dye-based inks, meaning that less pigment-based ink is required to create the intensity of color. However, adhesive components are necessary to use along with pigmented inks to prevent removal of the pigment from the surface by mechanical abrasion or chemical leaching.
The industrial importance of pigment-based inks has increased in recent times. This is driven, in part, by the development of many new synthetic substrates that are incapable of being printed with conventional solvent-based or water-based inks, and consumers' preferences that their goods be printed with brand identifiers, aesthetically pleasing designs or functional markings. In order to adapt pigment-based inks for use in a variety of applications, namely low surface tension substrates, others have employed high loads of volatile organic compounds (“VOC's”), thereby reducing the static and dynamic surface tension of the inks. However, volatile organic compounds such as alcohols, esters, ketones, aromatics and aliphatics create environmental hazards in their production, disposal and use. They are also expensive. One example of an ink used on an a low surface tension substrate is set forth in U.S. Pat. No. 5,458,590 to Schleinz et al., which employs a solvent blend to impart the desired surface tension to the ink.
It has also been recognized that adding small amounts of wax to a polymer adhesive improves the dry rub properties. This is set forth in U.S. Pat. No. 5,458,590 to Schlienz et al, which shows using 0.5-5.0% wax, and in USPA 2007/0100025A1 to Steiner et al, which shows using 0.1 to 2.0% waxes.
Still others have devised methods to adhere ink to low surface tension substrates, such as surface pre-treatment via corona discharge treatment, plasma treatment or use of a primer, as set forth in USPA 2006/0246263 to Yahiaoui et al.
For an ink to be useful, it needs to be in a medium capable of binding with a substrate, either chemically or physically. Where physical binding is desirable, the ink's medium may have adhesive characteristics, and may be somewhat flexible to withstand distortions of the substrate. The flexibility of an aqueous polymer is typically expressed as its glass transition temperature, or Tg. Lower Tg's generally correlate to greater elongation without fracturing. The elongation property is significant in adhesive and coloring because the flexibility/elongation of a formula's polymer affects rub resistance. Specifically, flexibility and softness associated with lower Tg polymers provide a high degree of grab and tack, which is expressed as a high coefficient of friction (CoF). The higher the CoF, the more likely the polymer is to “grab onto” and be “abraded off by” some other substrate or surface, thereby lowering the composition's dry rub resistance. Thus, in conventional inks, the desirable properties of adhesion and flexibility are at the expense of rub resistance. Alternatively, improving rub resistance conventionally creates adhesion and flexibility problems.
Thus, there remains a need for a substrate having improved crockfastness through the use of a water-based ink which is environmentally friendly. There remains a need for a water-based ink that is useful on a variety of substrates including those with low surface tensions, which has desirable wet and dry rub properties, resulting in improved crockfastness of substrates.